EVALUATION OF MYOCARDIAL VIABILITY WITH TC-99M HEXAKIS-2-METHOXYISOBUTYL ISONITRILE AND I-123 PHENYLPENTADECANOIC ACID AND SINGLE PHOTON-EMISSION TOMOGRAPHY

The detection of viable myocardium in infarcted regions, i.e. hibernating myocardium, is a major goal in clinical cardiology today. We applied combined planar and single photon emission tomography (SPET) to the non-invasive estimation of the left ventricular ejection fraction (LVEF), myocardial blood flow and free fatty acid uptake in the heart. Of the 31 patients with coronary artery disease, 25 (81%) had had a previous myocardial infarction. All patients had at least one persistent perfusion defect on the stress-rest technetium-99m hexakis-2-methoxyisobutyl isonitrile (Sestamibi) study, and the results revealed 57/124 (46%) persistent perfusion defects. As a part of the perfusion study, the LVEF was measured at rest using the first-pass Tc-99m-Sestamibi injection, and the mean LVEF was 47% +/- 9% (mean +/- 1 standard deviation). Iodine-123 phenylpentadecanoic acid (I-123-pPPA) imaging at rest was performed within 2 weeks from the perfusion study. Then 6-mm transaxial, sagittal and coronal slices of the perfusion and I-123-pPPA studies were reconstructed. The bull's eye displays of the coronal slices were visually surveyed and divided into 4 quadrants: anterior, lateral, posterior and septal. The following image score was used: 0 = fixed defect, 1 = partial uptake and 2 = normal uptake. Moreover an index of metabolic reserve (MR) was calculated by dividing the bull's eye of the I-123-pPPA study by the bull's eye of resting Tc-99m-Sestamibi, and its maximum value was normalized to 100%. Fourteen segments (25%) had a normal 1231-pPPA uptake with a MR value of 96% +/- 8%. Twenty-two segments (39%) had a partial I-123-pPPA uptake with a MR of 74% +/- 20%, whereas 21 segments (36%) had no I-123-pPPA uptake and a very low MR of 36% +/- 34%. There was a highly significant correlation (r = 0.70) between LVEF and MR. These findings suggest that it is possible to identify viable myocardium by measuring contractile function (first-pass, multiple-gated Tc-99m-Sestamibi) and myocardial perfusion (stress-rest Tc-99m-Sestamibi) and by combining these parameters with myocardial fatty acid uptake (I-123-pPPA) studies.